In Vitro Comparison of Cone Beam Computed Tomography with Digital Periapical Radiography for Detection of Vertical Root Fracture in Posterior Teeth.

Statement of the Problem The diagnosis of vertical root fracture (VRF) is a challenging task. Purpose This in vitro study compared cone beam computed tomography (CBCT) imaging with digital periapical radiography (DPR) made by three different horizontal angels (20°mesial, 0° and 20° distal) for accurate diagnosis of VRF. Materials and Method Among 120 posterior teeth included in this study, 60 were vertically fractured. Fractured and non-fractured teeth were randomly distributed into three groups defined as group 1 with no filling in the root canal, group 2 with gutta-percha in the canal, and group 3 with the intracanal post. All samples were placed in a dry mandible and imaged with CBCT and DPR techniques. Two blind observers investigated the images. Results CBCT had higher sensitivity but lower specificity compared with DPR, except for the intracanal post group in which the sensitivity of DPR was higher; though the chi-square test showed the differences to be statistically insignificant. The sensitivity, specificity, and accuracy of CBCT and DPR were reduced in the cases that gutta-percha or post were present in the canal. Inter-observer agreement was higher for CBCT. A set of three DPRs with different horizontal angels were significantly more sensitive for VRF recognition than a single orthogonal DPR. Conclusion Based on our results, there was no significant difference between CBCT and a set of three DPRs with different angulations for VRF detection in posterior teeth. Therefore, it is suggested to consider DPRs with three different horizontal angels (20°mesial, 0° and 20° distal) for radiographic evaluation before CBCT examination.


Introduction
Vertical root fracture (VRF) is a longitudinal crack extended along the tooth root. [1] Previous root canal treatment and placement of a post, especially a short one, have been reported in most of the extracted teeth with VRF. [2][3] The diagnosis of VRF is nearly always a challenging task. A series of clinical and radiographic signs alo-ng with the clues in the patient's history and complaints suggest VRF in a tooth. But none of these signs are pathognomonic [4] and the diagnosis can only be confirmed by direct inspection of the fracture line in the suspected tooth. [1] Poor prognosis and progressive bone resorption leave no option but to extract the fractured tooth in most cases. [1] In order not to waste more cost and effort on further treatments and also to prevent more destruction in the surrounding tissues, it is important to differentiate VRF from other possible pathologic conditions. [5] The radiolucency of the fracture line is one of the first radiographic signs. [1,[5][6] Most of the time, it is hardly detectable in periapical radiographs because the horizontal angle between the projected beam and the fracture plane must be less than 4 degrees. [6] In addition, superimpositions may prevent proper detection of the fracture line. In some reports, the cone beam computed tomography (CBCT) is considered superior to the periapical radiography (PR) for VRF recognition, [7][8] however; Kambungton et al. [9] found the difference to be insignificant. Furthermore, higher doses of radiation exposure and costs in comparison with intra-oral radiography [10] and occurrence of artifacts in the presence of radio-opaque filling materials may limit CBCT application. [11] Da Silveria et al. [12] reported that the sensitivity and specificity of PR for VRF diagnosis in single-rooted teeth with opaque root filling material and post were improved by using different horizontal angles and this approach should be considered prior to CBCT application. Kambungton et al. [9] similarly concluded that PR examination with three different horizontal angles was more effective than a single orthogonal projection in single-rooted non-filled teeth. Despite several researches, it remains unclear whether it is prudent to prescribe CBCT for VRF diagnosis. VRF is more prevalent in posterior teeth. Studies focusing on posterior teeth might be more practical. [5] The purpose of this study was to compare the accuracy of CBCT and digital periapical radiography (DPR) taken at three different horizontal angles for detection of VRF in root filled and post cemented posterior teeth.

Materials and Method
This analytical cross-sectional study was approved by the Ethics Committee of Isfahan University of Medical Sciences.

Sample preparation
This study used 120 extracted intact human mandibular posterior teeth (60 premolars, 60 molars). After debridement with ultrasonic scaler (Ultrasonic Cleaner LX; Faraz Mehr Isfahan Co., Iran), root surfaces of the extracted teeth were stained with 1% methylene blue and inspected with a 5× magnifier. Teeth with any previous crack or fracture were excluded.
After the preparation of a straight-line access, cleaning and shaping of the canals were completed with passive step-back technique by using #10 to 40 K-type files (Dentsply-Maillefer; Ballaigues, Switzerland) and #2 and 3 Gates Glidden drills (Dentsply-Maillefer; Switzerland). Forty teeth were selected randomly and the root canals of the 80 remaining teeth were obturated through the lateral condensation of #20 to 45 guttapercha cones (Aria Dent; Tehran, Iran) and by using AH26 root canal sealer (Dentsply Tulsa Dental; Switzerland). After complete setting of the sealer, the guttapercha of the premolar canals and one of the molar canals were removed by using #2 or 3 Peeso reamer drill (Dentsply-Maillefer; Switzerland) in a way that at least 4 mm of gutta-percha remained at the apical end. Half of the filled and unfilled teeth were randomly selected.
Then, a custom made pin was inserted in the vacant space of the canal. By using a hammer, intermittent strokes were applied in a controlled manner until fracture occurred. The teeth with separated parts were excluded. The presence of fracture was confirmed by using staining method described above. The orientation of fracture line was recorded.
The fractured teeth were randomly distributed into three groups. Samples in group 1 had no filling material in the canals, group 2 had a prefabricated screw-type post (Svenska Dentorama AB; Stockholm, Sweden) suitable for the canal in size and length which was cemented with zinc phosphate cement (Prime-dent; Chicago, USA), and in group 3, the canals were re-filled with gutta-percha (Aria Dent; Iran). Non-fractured teeth were randomly divided into three groups similar to the fractured teeth. All groups included an equal number of molars and premolars (10 molars and 10 premolars).
Finally, all the access cavities were filled with dental amalgam (Aristaloy; Birmingham, UK). In order to prevent intrusion of amalgam into the non-filled canal spaces during condensation, a small piece of cotton was placed in the canal orifice before filling the access cavity.
A dry human male mandible with relatively huge tooth sockets was selected. In order to adapt more efficiently to various root shapes, the sockets were enlarged by the use of a long cylindrical carbide bur (D&Z; Wie-  CBCT: cone beam computed tomography; DPR: digital periapical radiography; 1: observer 1 (radiologist); 2: observer 2 (endodontist); C: consensual report of the two observers sbaden, Germany) and a high speed dental hand piece (Henry Schein Company; Prague, Czech Republic) under water coolant system. Samples were randomly selected from the six groups, placed into sockets, and fixed with red wax.

Imaging
DPR was made from each placed tooth at three horizontal angles. In the first group, the X-ray beam was perpendicular to the tooth long axis and receptor (orthogonal), the second group was imaged at 20° mesial angulation, and the third group was imaged at 20° distal angulation. The radiologic images were made using an in- The observers were allowed to change the contrast, brightness, invert, and zoom options on all images. Two involved observers were educated and calibrated in a pilot study to detect VRF in CBCT and DPR images. In addition to individual reports of each observer, a consensual diagnosis was reported for each tooth based on the diagnosis of both observers. In cases of disagreement between the two observers, they were asked to reach an agreement.

Data analysis
Sensitivity (correct detection of the fractured teeth), specificity (correct detection of the non-fractured teeth), and accuracy (correct detection of non-fractured and fractured teeth) were calculated for CBCT and DPR images inspected by each observer separately in the three groups. Chi-square test was used to assess the difference between sensitivity and specificity values. Kappa index was used to assess inter-observer agreement (p< 0.05) and also to assess consensus of CBCT and DPR versus the gold standard in each of the three groups. The data were analyzed by using SPSS software for Windows (version 16.0; SPSS Inc.).

Results
Generally, CBCT had higher sensitivity, but lower specificity compared with DPR (Table 1). However, Chisquare test showed the difference to be insignificant (Table 2).  The overall sensitivity and specificity of orthogonal DPR were 0.53 and 0.85 respectively. By using three angulations, the sensitivity of DPR was improved to 0.75 but the specificity was reduced to 0.80. Chisquare test showed the difference between the sensitivities were significant (p= 0.013); whereas, the difference between the specificities was insignificant (p= 0.471).

Consensus of CBCT and DPR versus the gold standard
was higher for teeth with no canal filling than those in the two other subgroups. Higher agreement with the gold standard was obtained for CBCT compared with DPR in no filling and gutta-percha groups. But in the post group, the kappa value showed higher agreement for DPR (Table 3). Inter-observer agreement was higher for CBCT (κ= 0.882, p< 0.001) in comparison with DPR (κ= 0.732, p< 00.1).

Discussion
Based on our results, CBCT was more sensitive but less specific compared with DPR for detection of VRF in root filled posterior teeth; however, the difference was insignificant. A systematic review has recently mentioned that in vivo studies reach higher values of sensitivity for CBCT rather than for DPR; which is in common with our results. However, the difference was stated to be significant. Moreover, the specificity of DPR was reported to be higher, but comparable with that of CBCT. [13] Regarding the higher radiation dose of CBCT, [14] our study supports the application of PR with three different horizontal angels in the cases suspected to VRF. In the cases with no filling material in the canal, the fracture was detected more probably and CBCT was more accurate. In the presence of guttapercha or post in the canal, the sensitivity and specificity of both imaging modalities were decreased.
The sensitivity of CBCT was higher in no filling and gutta-percha groups, but lower in post group. This finding indicates that the fracture is more likely to be discovered in periapical radiographies rather than in CBCT when a cemented radio-opaque post exists in the canal (Figure 1).
Consistent with the findings of Kambungton et al., [9] the difference was insignificant; while, Hassan et al. [7] reported a significant difference between the sensitivity of these two modalities. CBCT provides a threedimensional (3D) image of the tooth; so the fracture is more likely discoverable in a 3D image like CBCT rather than in a two-dimensional image obtained by PR.
Accordingly, the sensitivity values are greater for CBCT.
As previously demonstrated, the sensitivity of Our results corroborate the previous findings that reported DPR was more specific than CBCT for VRF diagnosis in root-filled teeth. [7,17] Inconsistent with a study that reported the significance of the difference between the specificity of the two modalities, [17] our findings confirmed the insignificance of this difference.
[7] Higher DPR specificity is probably due to the two-   [21] reported. The images in the current study were reviewed by only two observers; while more observers are needed to conclude more confidently.
The tooth missing structure should be restored after root canal therapy; metal restorations are commonly used to achieve this purpose in posterior teeth. [22] Similar to the root filling materials, these restorations can cause streaking artifact in CBCT images and may influence its diagnostic value. To our knowledge, none of the previous in vitro studies restored the teeth with metal restorations. To achieve more similarity to the real clinical conditions in this study, after root canal therapy, the access cavity was filled with amalgam as a dense metal restoration. Nonetheless, we did not evaluate the effect of the coronal filling on VRF diagnosis. Further studies might be needed to find out its possible effects.
The present study did not measure the width of the fracture, either. Wider cracks are significantly more detectable in CBCT. [14] Obtaining different values of sensitivity and specificity in studies with no control over the fracture width might be ascribed to different methodologies which resulted in different crack widths. [17] Moreover, the lower values reported in an in vivo study compared with in vitro investigations may be due to the greater width of an artificially induced fracture. [15] Although the fracture width is a confounding variable over which we had no control, it must be considered that it is difficult to measure the fracture width in many teeth.
Due to dedicated traits and application of different CBCT devices, the results of this study can be attributed to the employed system. Using other machines may yield different results.

Conclusion
There was no statistically significant difference between the CBCT and a set of three PRs prepared at different horizontal angels (20°mesial, 0°, and 20° distal) for in vitro VRF detection in posterior teeth.